The present invention relates to a method and apparatus for detecting the presence of cancerous tissue and more particularly to a method and apparatus for detecting cancerous tissue using native visible luminescence.
Because a sufficiently effective method has not yet been developed to prevent cancer, cancer research has focused on the most effective ways to cure an organism that is diagnosed as having a cancer. As different as the various forms of treatment have been--ranging from excision to radiation to chemotherapy--all treatments have relied on one crucial step, detection of the cancerous tissue. The importance of detection cannot be stressed enough. Early detection not only indicates the presence of a cancer but also may give an indication as to where the cancer originated and as to what type of treatment will be the most safe and effective method. Early detection can provide such benefits because it reveals the state of maturation of the cancer cell. Cancer cells are clonal cells of a single "founder" cell that is the result of some mutation of the normal cell for the particular tissue. As a result of the mutation, the founder cell replicates and divides, eventually forming a mass of cells called a tumor. Tumors are harmful to an organism because they proliferate at a metabolic rate that exceeds that of the normal neighboring cells. As a result, the tumor grows at the expense of the normal neighboring tissue, ultimately destroying the normal tissue. One of the reasons why it is so difficult to completely cure an organism of cancer is that cancer cells have the ability to disseminate throughout the organism via lymphatic or circulatory systems and to create new tumors where they arrive. However, this ability to disseminate comes only to those cells that have lost the characteristic membrane glycoproteins of the mutated tissue. For this reason, it takes a while before cancer can spread. An advantage to early detection is that the cells can be examined for characteristic properties such as cell size and shape to determine the source of the cancer cells.
Clearly, the importance of an accurate technique that can be utilized in vivo or in vitro cannot be minimized. The advantage of an in vivo and in vitro technique is that sensitive tissue may be tested, relatively undisturbed, for example, with the use of an inserted optical fiber probe.
Presently, the diagnosis of cancer mainly relies on X-rays, nuclear magnetic resonance, nuclear radiation or invasive methods based on chemical laboratory analysis and biopsy. In view of the dangerous side effects of X-rays, nuclear radiation, and biopses it appears that a definite need exists for a new technique for detecting cancer which can either eliminate or reduce the necessity of X-rays, nuclear radiation, and biopsies.
Although there exist many effective methods for detecting cancer, very few methods are based exclusively on the intrinsic properties of the cell and, as a result, interfere with normal tissues. For example, Hematoporphyrin derivative (HPD), which absorbs preferentially to cancerous tissue, is currently employed as a photosensitizer of tumors for photoradiation therapy. Unfortunately HPD interfers with normal tissue and does not make a good in vivo technique for detection. Flavins and porphyrin found in abundance for their effectiveness at transferring electrons in subcellular organelles known as mitochrondria are known to fluoresce in the visible light portion of the luminescence spectra.
Optical spectroscopy and laser technology offer new possible techniques for detection and characterization of physical and chemical changes which occur in diseased tissue, either invivo or invitro. This lends itself to a new approval for diagnosis of pathological changes in tissue.
The present invention is based, at least in part, on the discovery that the fluorescence spectra profile of cancerous tissue is different from the fluorescence spectra profile of normal tissue, the discovery that the fluorescence peak is blue-shifted (shifted to lower wavelengths) and in other samples red-shifted (shifted to longer wavelengths) in areas corresponding to flavin and porphyrin peaks and that the red peaks are reduced in intensity. Because this blue-shift (or red-shift) in the fluorescence spectra is an intrinsic property of the tissue, normal tissue is unaffected, making the monitoring of these fluorescence spectra an especially safe in vivo technique. A possible explanation for the blue-shift (or red-shift) and change in fluorescence spectral profile of cancerous tissue is that the flavins and porphyrins are in different environments that effect the fluorescence of these molecules. Flavins maybe blue-shifted (or red-shifted) when a protein closely associated to the flavin acquires net positive (blue-shift) or negative (red-shift) charge relative to its native state. Porphyrins, which fluoresce only in cancerous tissue are probably in the dissociated state since this is the only form that fluoresces. The abundance of free porphyrins in cancerous tissue may result from a reduction of the metal ion that serves to build the porphyrins in the proteins. Self absorption by hemoglobin molecules may cause the complex profile in normal tissue.
The discovery that certain biological molecules fluoresce differently in cancerous and non-cancerous tissue and that spectral changes in shape and shift to the blue (or red) for these molecules present a sufficient criteria for determination of cancerous tissue.
The present invention is also based in part of the discovery that the excitation spectra are different for normal and cancerous tissue.
In U.S. Pat. No. 2,437,916 to W. F. Greenwald there is described a technique for examining living tissue which involves illuminating the tissue with a beam of light and then measuring the intensity of the reflected light at certain wavelengths ranges using a phototube and different colored filters.
In U.S. Pat. No. 3,674,008 to C. C. Johnson there is described an instrument which quantitatively measures optical density of a transilluminated body portion. The instrument comprises a controllable, relatively low-frequency oscillator generating pulses which are applied to a light source through a first expand and delay circuit. A light-conducting source to one side of the body portion and a similar means optically couples another side of the body portion to a light detector. Alternatively, the light source and detector may be placed directly on the body portion. After compensation for ambient light, the output of the detector is coupled to a sample and hold circuit which is triggered by the controllable oscillator through a second expand and delay circuit. The stored signal in the sample and hold circuit is proportional to transmittance and calibrated display means. Methods of using the instrument in diagnosis are discussed, as are further applications to spectrophotometeric determinations.
In U.S. Pat. No. 3,963,019 to R. S. Quandt there is described a method and apparatus for detecting changes in body chemistry, for example, glycemia, in which a beam of light is projected into and through the aqueous humor of the patient's eye. An analyzer positioned to detect the beam on its exit from the patient's eye compares the effect the aqueous humor has on said beam against a norm. An excess or deficiency of glucose present in the aqueous humor produces a corresponding positive or negative variation in the exiting beam and thereby indicates a hyper or hypo glycemia condition in the body chemistry of the patent being tested.
In U.S. Pat. No. 4,029,085 to D. P DeWitt et al there is described a method for determining the bilirubin concentration in the blood serum of a person from measurement of the spectral reflectance of the skin. The disclosed method detects the severity of jaundice, common neonatal condition, and enables determination of the type of treatment regimen needed to prevent the billirubin level from becoming sufficiently high to cause kernicterus which can result in brain damage. The method includes measuring the reflectance of the skin within a predetermined frequency spectrum, and more particularly, at a number of specific wavelengths in the visible portion of the spectrum.
In U.S. Pat. No. 4,290,433 to Robert R. Alfano there is described a method and apparatus for detecting the presence of caries in human teeth using visible luminescence. A region to be examined is excited with a beam of monochromatic light. The intensity of the visible light emitted from the region is measured at two predetermined wavelengths, one where the intensity dependence of the spectra is about the same for caries and non caries and the other where the relative intensity changes significantly in the presence of caries. A signal corresponding to the difference in the two intensities is obtained and then displayed. By first determining the magnitude of the difference signal at a nondecayed region, any increases in the magnitude as other regions are probed on the discovery that the visible luminescence spectra for decayed and nondecayed regions of a human tooth are substantially different and that the differences are such that visible luminescence from teeth can be used to detect the presence of caries.
In Medical and Biological Engineering, Vol 6, No 4 August, 1968, pp. 409-413 there is described a technique for tissue identification during needle puncture by reflection spectrophotometry.